The objective of this project is to evaluate the impact of severe chorda-lingual nerve injury on gustation and taste bud density, specifically the capacity of human subjects with unilateral nerve injury to detect and scale the strength of different concentrations of citrate applied to spatially- matched, isolated, discrete regions of the anterior tongue tip. The anatomical characteristics of fungiform taste buds within the same site tested for citrate taste perception will be investigated using a non- destructive staining method and videomicroscopy. It is hypothesized that severe injury to the chorda-lingual nerve in humans results in the loss or depletion of taste sensibility due in part to denervation atrophy of fungiform taste buds. Information from these studies will provide a method to diagnose hypogeusias following injury to the chorda- lingual innervation in humans and should thus contribute to the understanding and treatment of taste disorders which involve the chorda- lingual nerve. Citrate detection thresholds and subjective strengths of taste intensity will be assessed in healthy men and women with unilateral severe chorda- lingual nerve injury as a result of dental or maxillofacial surgery. A two-alternative forced choice, modified staircase procedure will be used to derive threshold. Cross-modal magnitude matching functions for taste intensity judgement will be obtained for five concentrations of citrate, and measures of perceived strength will de determined. The right and left tongue tip surface will be tested to assess the effect of selective nerve damage on citrate taste perception. Citrate solutions will be delivered to an enclosed, self-retained chamber reinforced to the surface of the right/left tongue tip so that only a discrete and isolated surface area of the tongue will be tested. The taste buds bathed by stimuli within the chamber will be distinguished by methylene blue stain and recorded by videomicroscopy. The number of fungiform papillae and pores per unit area will be determined so that the relationship of discriminative taste performance for a known number of taste buds can be examined. Comparisons of global (i.e., whole mouth) threshold and suprathreshold scales of citrate taste intensity will be made to elucidate the effect of unilateral nerve injury on global taste perception.